U.S. Pat. No. 7,639,026, and its priority document, to Shell et al issued 29 Dec. 2009 is hereby incorporated by reference in its entirety and provide background to this invention.
The testing of integrated circuit devices is performed to ensure that such devices, when sold to a customer, are of as high a degree of quality as possible. Various types of test apparatus have been utilized over the years to accomplish testing. Typically, a tester includes a printed circuit board which has defined thereon a plurality of conductive traces. These traces on the circuit board, or load board, are associated with corresponding functions of the test apparatus.
In order to accomplish testing, it is necessary to interconnect a lead, in the case of a leaded device under test, or a pad, of a nonleaded device under test, to a corresponding trace on the load board. A test set or test socket having a plurality of contacts is interposed between the device under test and the load board in order to effectuate interconnection. A contact is engaged, at an upper end thereof, by the lead or pad of the DUT, depending upon the type of DUT being tested, with its corresponding trace on the load board. A lower end of the contact is in engagement with a trace on the load board.
As technology has progressed, the size, shape and electronic properties of contacts have evolved in response to the construction of test sets and load boards and the architecture of devices to be tested. At one time, it was considered necessary to have a wiping action at the various locations of engagement of the contact ends by the lead or pad of the DUT and the pad on the load board.
Such wiping action was deemed to facilitate a good transmission path through the contact because of a good connection at either end thereof. It has become more apparent, however, that the measure of wiping action formerly considered necessary to maintain a good transmission path need not be of a degree as was formerly believed. Further, it has been recognized that excessive wiping action can damage component parts at the various points of engagement of the contact, and thereby significantly decrease the life of the test socket and tester load board. Consequently, various attempts have been made to minimize abrading of one surface relative to another. Various elastomeric mounting means have been devised in an effort to minimize abrasion and consequent deterioration of components.
Another problem which has been discovered is the diminishment of effectiveness of testing as a result of the employment of matte tin on leads and pads of various types of DUTs. Such a material is applied to DUT components which facilitate soldering to an ultimate host circuit board. Because of its softness, however, it easily can progressively become adhered to the contact which the DUT engages as rubbing across engaged surfaces occurs during the testing function. Eventually, matte tin can build up to the point where signal integrity through the contact can become diminished.
In addition, it has been determined, that the tip of prior art contacts has drawbacks. First, wiping action of such tips may cause it to miss its target contact point through all or part of its rocking action. Second, the rocking action may cause significant wear on the contact tip. Third, the wiping action can release debris which is electrically conductive and thus result in test failure, either from shorting across contacts, or by changing the high frequency response of the text fixture due to build up of metallic debris.
It is to these dictates and shortcomings of the prior art that the present disclosure is directed. The present invention is a contact having a structure which minimizes tin buildup on the contact.